Slack-cleaner2

bug fixes
* c77

new features:
* add `SlackMessage.dt` and `SlackMessage.thread_dt` as datetime objects of the timestamps. the default print has also changed to use the dt isoformat

Bugfix Release

the list_files api uses a different type of pagination than other endpoints. This bugfix should make sure the right one is being used

Lazy Evaluations and Rate Limit Handling

major refactoring within the code to lazy fetch channels, channel members, and users. This leads to an improved scalability and faster start up time.

* Users are fetched one by one unless all users are iterated over
* Channels members are only fetched upon access of the `.members` attribute
* Channels are fetched upon access

in addition, there is support for listing and deleting message reactions

add support for adding `team_id` for organization wide tokens

add new "show_files_hidden_by_limit" flag for listing files

* workaround for slack error: `fetch_members_failed` by handling it gracefully and not trying to fetch members of archived channels